Waveguide switch



Oct. 4, 1960 H. .1. RIBLET 2,955,268

wAvEGUIbE swTcH Filed March e, 1958 FIG. 2B

INVENTOR.

HE/V/QY d. E/ELET United States Patenti() WAVEGUIDE SWITCH Henry '.I. Riblet, 3'5 Edmunds Road, Wellesley, Mass.

Filed Mar. 6, 1958, Ser. No. 719,672

Claims. (Cl. S33-98) power is often so great that the mixer crystal of the 'in- .active set is burned out, the T-R tube of the inactive set then'being disabled. To alleviate this d-iiculty, it'has been-'suggested that a shorting plate be positioned between A.the antenna and mixer when the'set is inactive. However, `a slot in a wavegiude wall permitting the projection and withdrawal of a shorting stub seriously interferes with the impedance properties of the waveguide. Due to mismatches,'the overall system sensitivity is' appreciably reduced. Y

The present invention contemplates and has as a primary object the provision of a waveguide switch for selectively controlling the ow of microwave energy through the waveguide without appreciably disturbing its impedance characteristics in the open position.

According to the invention, the electric eld within the waveguide is selectively shorted by the extension through small openings -in the waveguide wall, of a plurality of coplanar, thin conducting rods aligned parallel to the electric eld. The spacing between `open-ings and-rods is large compared -to the cross-sectional dimensions of either. As a result, these openings cause virtually no interference with the charge distribution along the waveguide wall with the switch in the open position.

A feature of the invention resides in locating an impedance matching element within the waveguide opposite the openings. This reduces the distance traveled by the rods dur-ing switching and, consequently, the switching time. Yet, the open switch causes negligible effect on the waveguide impedance characteristics.

Other features, objects and advantages of the invention will become apparent from the following specication when read in connection with the accompanying drawing in which:

Fig. 1 is a perspective view of a short waveguide section having a solenoid-actuated waveguide switch arranged according to the invention;

Fig. 2A is a cross-sectional view of the waveguide switch taken along plane 2 2 of Fig. l, illustrating the switch in the closed position;

Fig. 2B is the same view as Fig. 2A, but with :he switch I open;

Fig. 3A is a fragmentary end view of the waveguide switch, showing the switch in closed position; and

Fig. 3B is the same view as Fig. 3A, but with the switch open.

With reference now to the drawing and more particularly Fig. 1 thereof, there is illustrated a perspective view of a solenoid-operated waveguide switching section. The

42,955,268 Patented Oct. 4, 1960 waveguide section 11 has end flanges 12 adapted for attachment to other waveguide sections by means of choke joints or other suitable well known coupling means. The top wide wall 13 is perpendicular to both narrow walls 14 and supports a lower housing 15- of the switch actuating mechanism. An upper cylindrical housing 16, attached to lower hous-ing 15, encioses a solenoid energized through leads 17.

Additional structural details are better seen by referring to the sectional view of Fig. 2 which exposes the actuating mechanism. The solenoid 21 surrounds a cylindrical cavity 22, which in turn accommodates compression spring 20 and magnetic plunger 23A. Thin coplanar, cylindrical rods 25 are rigidly suspended like the tines of a fork from a support 26, the latter being attached to the lower end of plunger 23 by an extension 24. As plunger 23 is displaced within the cavity 22, rods 25 slide through `openings 27 in the top wide wall 13. Their downward travel -is limited by a conducting plate 3-1 formed with steps 32 and 33 symmetrically disposed about its midpoint, and a plurality of appropriately spaced receiving openings 41.

Conducting plate 311 is in surface contact with lower wide wall 34 and is centrally disposed between and parallel to narrow walls 14. The length of each of the two end steps, measured along the guide, is approximately a -quarter of the wavelength of microwave energy normally v propagated in the waveguide system into which the switch is coupled. The steps are so positioned that cancellation of reections is effected over a relatively wide frequency lband when theswitch is open. For a discussion of suitable design techniques, reference is made to a paper by Henry l. Riblet entitled General Synthesis of Quarter- Wave Impedance YTransformers at page 36 of the IRE lTransactions on Microwave Theory and Techniques for January 1957, and'rnore specifically, to the iirst full paragraph on Page 40.

Figs. 2B` and SLB, show the switch open with rods 25 fully withdrawn from the inside of the waveguide, and section l11 trans-mits energy between adjacently connected waveguide sections without mismatch.

Figs. 2A and 31A show the switch closed with the rods 25 in contact rwith conductingplate 31. In this position f energy isinot transferred through section 11 but instead is substantially all reilected. As a practical matter, it has been observed that the rods 25 need not contact plate 31. In fact, better isolation has been obtained by locating the rods with their ends separated from plate 311 by a narrow air gap.

In a representative application of the novel switch section between an antenna and a receiver mixer crystal, the downward pressure on stern 23 exerted by spring 20 forces rods 25 into the waveguide section when solenoid 21 is deenergized. 'Ihe rods 25 are withdrawn when solenoid 21 is energized. This is especially advantageous since leads 17 may be connected so that solenoid 21 is energized and deenergized when the associated radar set is turned on and olf, respectively. Should the radar lose power, whereby the T-R tube becomes inoperative, spring 20 would immediately close the switch to protect the mixer crystal.

When the switch is closed with rods 25- down, section 11 is eifectively divided into two adjacent, parallel waveguide sections characterized by cutoff frequencies above the frequency of the incident microwave energy. This creates a severe mismatch and virtually all the incident microwave energy is reflected.

When the switch is opened -by withdrawing rods 25 from the interior of section 11, the stepped plate 31 prevents mismatch. This occurs because reflections from the vertical edges of each of the two steps, separated as Wholly cancelled.

' plane parallel to Saidnarrow walls and including said A compact fast-operating waveguide switch has been I described for selectively isolating microwave circuits while .impedance ;rismatches. An .band '.switch .constructedxasvshown :annif-described. exhibits ea VSWR-.of :less than 1.1 overthebandffrom;8500.mc. ,to19r600fn1c. with thenswitch open.

Numerous .modifications i of and :departures from the specc embodiment describedeherein may b e practiced Lbythose :skilled in the art=without departing fromthe inventive concepts. Consequently, the invention is to .be `construed as limited only bythe rspiritand scopepofihe `appended claims.

Whatis claimedis:

l. .A :microwave ,switch :.cornprising, 'ra waveguidev sec- -tion capable.- ofpropagating microwave `energy .having .a transverse relectric ield, -said waveguide :section having an outerconducting Walliformedwithaplurality of small .openings 'on ag'linegparallel tothe waveguide section-axis `and ys eparated=:bya distancergreater than thedimension along.-saidlinefof anyone of -saidopenings5 andan .oppositely disposedconductingtwall having a thin'nwardly extending .conductive g plate, -the inner edge .of said con- .ductivegplate-being arranged oppositely of andparallel to said line of small openings, a plurality of conducting 'rods normally. positioned within said waveguide in engagement wwithsaid --inneredgeof said. conductive plate andpa-rallel rto...the.`direction .of said electric eld in :a .plane Y, along .said axis, .said -plane eiectively dividing theinternal volume of said.waveguide.into adjacent waveguide .sections .hav- .ing .cutoi `frequencriesabove the frequency of isaid; micro- .wave energy, rand means .-for selectively fdisplacingsaid Arods .through Vrespective ones .of .said openings between `said :position within and a `position `without said wave- .guide section, .said conductive `plate 'being arranged tto .minimizefattenuation ofsaidrmcrowave `energy with-said :rods displaced to-,said position without said waveguide.

l.2. A microwave switch comprising, `a'rectangular:waveguide-having` a-pair fparallelV wide wallsjperpendicular to a pair of parallel narrow walls, a rst=.off saidwide -.walls..formed .with afplurality of vsmallopenings along a Vline Aperpendicularlyfbisecting the width ofsaid'rstfwall, :said .opcningsbeing separatedby a distancegreaterthan the dimension alonglsaidline ofanyone of saidiopenings, impedance matching. element formed of arconducting `r`plate .incontact with ithe second .of `said -wide :walls and .openings,.a plurality. ofconductingmods .adaptedtoreside within said waveguide parallel to said narrow Walls in the space between said plate-and said openings, and means for selectively displacing said rods through respective ones of said openings between a position within said space and a position outside said waveguide.

3. Apparatus lin accordaneewwith claim 2 wherein said conducting plate is formed with 4at least one pair of steps separated alongtheuaxisv-'of fsidl waveguide, each step being. approximately .one-.quarter-wavelength long measured along'the axis f said waveguide.

4. Appanauxsfin :acrdance'fwithtclaimmnd further comprising, a plungercarrying a support member, said rods extending fromsaidtsupportrmenben said support member being parallel to said wide walls, a solenoid surrounding said plunger, and resilient means for forcing said support member against said first wide wall.

35 A microwaveizswitch xcompris'ing, :a waveguide seo- -tionzforfnormallypropagatingmicrowavefzenergy:having-a -transverse :electric field-fa ithin conducting plate=rdisposed -withinzsaid ssection valanga the i direction-tof normal energy :propagation andparallel to :said electric field, a .plurality of thin conducting rods adapted to :reside with-in :said awaveguideiinzdre plane :including rsaid .conducting plate, y-tlIe-reby .effectively fzdivijding said :section l.into 'adjacent twaneguideshaving cutoi requencies above-.the frequency of said normallyspropagated microwave :energy,..and'means l foriselective'ly` displacing :said-rods between said yposition :spaced ifrom: said..i first wide iwall, .saidplate .being-.in 'a :within v.and raspos'rtion ioutsidezsaid waveguide section,=1 said :conducting plate vincluding rmeans for `preventing :im- .gpedancetmismateh' vsithzrespectto:incidentenergyZatsad normally propagatedvmicrowave frequency vkwhen :said rswitchsisopen.

.fl-References -zGited in the :tile of- ,Patent UNITED STATES PATENTS orHERREFnnE-NCES VBollinger et .-al.: NAbstract ...ofi application .Serial No. f94s944a PIblShedfNOVBmbeL-Zil, 1951, .640 OG. ,1032. 

